Relative Rate and Product Studies of the Reactions of Atomic Chlorine with Tetrafluoroethylene, 1,2-Dichloro-1,2-difluoroethylene, 1,1-Dichloro-2,2-difluoroethylene, and Hexafluoro-1,3-butadiene in the Presence of Oxygen

Abstract

Rate coefficients k1-k3 have been measured for Cl atom reactions with CF2═CF2, CFCl═CFCl, and CCl2═CF2 relative to k4 for CF2═CF-CF═CF2 at 293 ± 2 K. k4 was remeasured relative to Cl + ethane. Cl was generated by UV photolysis of Cl2, and other species were monitored by FT-IR spectroscopy. The measurements yield k1 = (6.6 ± 1.0) × 10(-11), k2 = (6.5 ± 1.0) × 10(-11), and k3 = (7.1 ± 1.1) × 10(-11) cm(3) molecule(-1) s(-1), respectively, and k4 = (8.0 ± 1.2) × 10(-11) cm(3) molecule(-1) s(-1) is proposed. These results are discussed in the context of atmospheric chemistry. Subsequent chemistry in the presence of oxygen leads to oxygenated products that are identified via their IR spectra, and possible mechanisms are discussed. The yield of CF2O from C2F4 is 93 ± 7%. Dichlorofluoroacetyl fluoride (CCl2FCFO) was observed as a product from CFClCFCl, and chlorodifluoroacetyl chloride (CClF2CClO) was observed from CCl2CF2 oxidation. C4F6 led to 66 ± 5% CF2O and 38 ± 3% OCF2CFC(F)═O. Reaction enthalpies and enthalpy barriers computed via CBS-QB3 theory help rule out some unfavorable mechanistic steps.